1. Field of the Invention
The present invention pertains generally to devices, assemblies and systems for backflow prevention, and more particularly to a compact, light weight, low maintenance double check valve backflow prevention apparatus of modular construction which provides low flow losses.
2. Description of the Background Art
Backflow prevention devices are widely used to prevent undesirable flow reversal under low flow, static or backpressure situations wherein clean upstream fluid sources can be contaminated by downstream fluid. Backflow prevention devices typically comprise one or two check valves, housed within a valve body, which undergo closure under backflow, backpressure or back siphonage conditions. The use of backflow prevention devices is generally required by law for cross-connected water supplies where potable water could undergo contamination due to flow reversal or back pressure conditions.
Currently used double check valve backflow preventers have proved deficient in various respects. Particularly, such back flow preventers are prone to relatively high flow losses due to the valve configurations and closure mechanisms employed, especially under low flow conditions. Further, back flow preventer assemblies typically require a bulky, heavy cast housing with a side port tube or extension and a separately cast port cover. This type of housing is expensive to manufacture and requires a substantial amount of space to accommodate the side port tube and cover. The check valves are typically bolted to seats within the housing, and can only be reached through the side port tube, which hinders access to the check valves. Maintenance and replacement of the check valves requires a person to reach through the side port tube and loosen bolts, compression rods or other internal hardware in order to remove the check valves, and thus tends to be a difficult and expensive operation.
Accordingly, there is a need for a backflow prevention apparatus which is compact and light weight, which is easy and inexpensive to manufacture, which does not have a side port tube, which provides easy access to internal check valves, which has check valves with simple, low-friction closure mechanisms, and which provides low flow losses. The present invention satisfies these needs, as well as others, and generally overcomes the deficiencies found in the background art.
The invention is a double check valve backflow prevention apparatus which provides low flow losses and which maintains a small positive pressure differential under static flow conditions. In its most general terms, the invention is a check valve apparatus, usable in a backflow preventer, which comprises a valve seat, a clapper pivotally coupled to the valve seat, a seal positioned to sealingly engage the clapper and valve seat when the clapper is closed against the seat, and a closure mechanism. The closure mechanism includes a first linkage element or member pivotally associated with the valve seat at a first pivot point located upstream from the seal, a second linkage element or member which is pivotally coupled to the first linkage element at a second pivot point, and which is pivotally associated with the clapper at a third pivot point, and a bias element associated with at least one of the linkage elements and configured to exert a closure force on the clapper.
By way of example, and not of limitation, the linkage elements of the closure mechanism preferably are elongated in shape, with the second linkage element being longer than the first linkage element. The first linkage element includes first and second ends, with the first end pivotally coupled to the first pivot point. The second linkage element likewise has first and second ends, with the first end of the second linkage element pivotally coupled to the second end of the first linkage element at the second pivot point. The second end of the second linkage element is coupled to the clapper at the third pivot point. The second linkage element may be bifurcated such that two halves of the second linkage element fit around the second end of the first linkage element.
The first pivot point is preferably associated with the valve seat, with the first pivot point being located at an upstream position with respect to the seal. Preferably, a rod or bar extends across the flow path defined by the valve seat, with the first pivot point defined by the rod and the first linkage element pivotally attached to the rod. The bias element preferably comprises a spring mounted on the rod extending across the flow path, with the spring configured to exert a force on the first linkage element. Preferably, detachable holders are included on the valve seat which allow quick and easy detachment of the rod for replacement of the spring and maintenance of the closure mechanism. In other embodiments of the invention, the first linkage element may be pivotally coupled to a valve housing or body which is separate from the valve seat.
The valve seat is preferably annular in shape and defines a flow path through the valve seat. The clapper preferable is hinged to a lower edge of the seat. The seal is preferably located on the clapper, and a lip is included on the valve seat and is configured to sealingly engage the seal when the clapper is closed. The seal may alternatively be positioned on the valve seat, with the clapper having a corresponding lip to engage the seal.
In the presently preferred embodiments, the invention is embodied in a backflow prevention apparatus comprising a valve housing and first and second check valves positioned within the valve housing. Various valve housing configurations may be used with the invention, including conventional cast valve housings having a side extension or flange and detachable cover mounted on the flange. More preferably, the backflow preventer apparatus of the invention comprises a tubular valve body with a flangeless side or lateral opening, and an external sleeve which slides or fits over the housing to cover the lateral opening and define a complete valve body. The first and second check valves fit within the valve body and are positioned with the first check valve adjacent the upstream edge of the lateral opening, and with the second check valve positioned adjacent the downstream edge of the lateral opening. The check valves are held against the edges of the lateral opening by means of a spacer, compression rods, or like separating element. An annular seal is included around the exterior of the valve seat of each check valve, and sealingly engages the valve housing when the check valves are in place.
The sleeve includes annular seals on its inner surface, and when the sleeve is in place over the lateral opening, the sleeve, housing, and annular seals on the sleeve define a complete, fluid tight valve body, with the check valves, spacer and lateral opening completely covered by the sleeve. The sleeve is held in place by the threaded end of a vent element, which extends through the sleeve and engages a corresponding threaded hole in the spacer or in the valve housing. The sleeve may alternatively be bifurcated or split, with each portion of the sleeve held to the valve housing by a threaded element.
In order to access the check valves, the vent is unthreaded and the sleeve is moved to expose the lateral opening in the valve housing. The spacer holding the check valves in place is removed, and the check valves are removed from the valve housing via the lateral opening. Since the lateral opening does not have a side extension or flange, the check valves are easy to reach, and no further disassembly is required for detaching and removing the check valves.
The dual linkage element closure mechanism of the invention and the positioning of the first pivot point at a location which is upstream from the location of the seal advantageously provides a small positive pressure differential under static and low flow conditions. The dual linkage element closure mechanism of the invention also allows the clapper to open at a relatively wide angle for greater flow when the check valves are open. The dual linkage element closure mechanism of the invention provides the advantageous flow properties of a magnetic closure mechanism without the fouling problems commonly associated with magnetic closure mechanism.
An object of the invention is to provide a backflow prevention apparatus which is compact and light weight.
Another object of the invention is to provide a backflow prevention apparatus which is easy and inexpensive to manufacture.
Another object of the invention is to provide a backflow prevention apparatus of modular construction.
Another object of the invention is to provide a backflow prevention apparatus which does not have a side port tube.
Another object of the invention is to provide a backflow prevention apparatus which does not require a formed port cover.
Another object of the invention is to provide a backflow prevention apparatus which allows quick and easy access to check valves for service, repair and replacement.
Another object of the invention is to provide a backflow prevention apparatus which mechanically produces a check valve closure force which simulates a magnetic closure mechanism without requiring the use of magnets.
Another object of the invention is to provide a backflow prevention apparatus which experiences minimal wear and requires low maintenance.
Another object of the invention is to provide a backflow prevention apparatus which has low friction losses.
Another object of the invention is to provide a backflow prevention apparatus which utilizes venturi-shaped check valves for optimal flow properties.
Another object of the invention is to provide a backflow prevention apparatus which maintains a small positive pressure differential under static flow conditions.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing the preferred embodiment of the invention without placing limitations thereon.